Experiment 4
Date:
Title:
Purpose: To determine the percent composition of a brass ball bearing.
Prelab questions:
1. What are the main two elements present in the alloy brass?
2. A. Write two single replacement re-dox reactions, one for each of the main two elements present in brass
reacting with Nitric acid?
B. Assign oxidation states and identify the substances oxidized and reduced?
C. Electrons flow from ________________ to ___________________.
3. What color are each of the products in an aqueous solution?
4. Which product’s concentration could be measured using a spectrophotometer?
5. A. If a 2.3 gram ball bearing were to be dissolved by 16 M Nitric acid, how many mL of nitric acid need to be
added?
B. Which element’s molar mass should you use to ensure you have enough Nitric acid? Why?
C. After dissolving, the solution is diluted to 100 mL, and the concentration of the measurable ion is found
to be .28 M. What is the percent composition of the ball bearing?
Procedure: Include a step by step procedure that will
a. Explain how you will turn the ball bearing into a solution, measure the concentration of that solution, and
determine the percent composition of the ball bearing.
Data Table:
Post Lab:
1. A. Place a dot on your graph in experiment 13 that will correspond to the absorbance of your copper II nitrate
solution produced here in lab 14. Using that graph try to estimate the molarity of the copper ii nitrate solution
produced in experiment 14.
B.
Using the equation of the line you experimentally determined in experiment 13, calculate the molarity of your
copper (II) nitrate solution.
C. Which method, graphical or algebraic, gave a more accurate result? Why?
2. A. Using your calculated molarity, show all work for determining the moles of Copper present in your brass ball
bearing.
B. Was the final volume of the copper (II) nitrate important? Would you have gotten better results with a larger
or smaller final volume? Why?
3. Show all work for finding the:
A. grams of copper present in your ball bearing
B. grams of zinc present in your ball bearing
C. percent composition of your ball bearing
4. Look up brass, and find the common ranges for the percent of copper in brass. Does your calculated value fall
within this range?
1.
Concentrated hydrochloric acid is not capable of dissolving copper metal, but obviously the concentrated nitric
acid is even though both acids are strong acids? Why? Which is the better oxidizing agent Cl1- or NO31-?
2. Explain how and why your calculated percent of copper in brass would change under each of the following
conditions.
a.
I added too much nitric acid.
b. Some of the copper nitrate splattered out of the beaker during dissolving.
c. The final copper II nitrate solution was diluted to 500 mL instead of 100 mL
d. The ball bearing was incompletely dissolved.
e. You measured the absorbance of your copper (II) nitrate at a blu wavelength instead of a red wavelength?
f.
Your b. b. had an inert corrosion on its surface.